The present invention is generally directed to a process for forming layers in electronic devices, such as in integrated circuit chips. The layers formed according to the present invention can be conductive layers, semiconductive layers, or insulating layers.
In general, an integrated circuit refers to an electrical circuit contained on a single monolithic chip containing active and passive circuit elements. Integrated circuits are fabricated by diffusing and depositing successive layers of various materials in a preselected pattern on a substrate. The materials can include semiconductive materials such as silicon, conductive materials such as metals, and low dielectric materials such as silicon dioxide. Of particular significance, the semiconductive materials contained in integrated circuit chips are used to form almost all of the ordinary electronic circuit elements, such as resistors, capacitors, diodes, and transistors.
Integrated circuits are used in great quantities in electronic devices, such as digital computers, because of their small size, low power consumption, and high reliability. The complexity of integrated circuits range from simple logic gates and memory units to large arrays capable of complete video, audio and print data processing. Presently, however, there is a demand for integrated circuit chips to accomplish more tasks in a smaller space while having even lower operating voltage requirements.
As stated above, integrated circuit chips are manufactured by successively depositing layers of different materials on a substrate. Typically, the substrate is made from a thin slice or wafer of silicon. The active and passive components of the integrated circuit are then built on top of the substrate. The components of the integrated circuit can include layers of different conductive materials such as metals and semiconductive materials surrounded by low dielectric insulator materials. In attempting to improve integrated circuit chips, attention has been focused upon reducing the thickness of the layers while improving performance.
As such, a need currently exists for a process for producing thin layers in electrical devices that are uniform and have improved electrical properties.
In general, the present invention is directed to a process for forming layers in electronic devices, such as integrated circuit chips. The process includes the steps of first placing a substrate in a reaction chamber. The substrate can be, for instance, a semiconductor wafer. The reaction chamber, on the other hand, can be a rapid thermal processing chamber that is heated by an array of light energy sources positioned outside the chamber. The chamber can also include other energy sources, such as a resistance heater placed adjacent to the substrate, a plasma source, a microwave device, and the like.
Once the substrate is placed within the reaction chamber, a precursor fluid is pulsed into the chamber. Once pulsed into the chamber, the precursor fluid is exposed to heat and/or light energy at low pressure causing the precursor fluid to convert into a solid layer on the substrate. In general, the precursor fluid can be any gas, vapor or flowable reactant capable of forming a desired coating within the chamber.
In accordance with the present invention, the precursor fluid is substantially exhausted and removed from the reaction chamber in between each pulse of the precursor fluid. As such, each pulse of the precursor fluid forms a very thin layer on the substrate. As each pulse enters the chamber, the layer on the substrate is built up to the desired thickness. Through this process, very thin but uniform layers can be formed on substrates without a significant amount of defects.
In most applications, it is important that the pressure within the chamber be maintained very low during introduction of the precursor fluid. For instance, the pressure in the chamber can be less than about 5 torr, particularly less than about 3 torr, and more particularly less than about 1 torr. Introducing the precursor fluid or reactants at low pressure facilitates formation of the solid coating on the substrate.
The precursor fluid introduced into the reaction chamber can be a gas, a liquid vapor, a mixture of gases, a mixture of liquid vapors, or a mixture of gases and vapors. Further, when the precursor fluid includes a mixture of reactants, the reactants can be mixed outside of the chamber or within the chamber itself. Through the process of the present invention, the precursor fluid can be used to form conductive layers, semiconductive layers, and dielectric layers. For example, the precursor fluid can be a reactive hydride for forming various layers such as metal layers. Particular examples of layers that can be formed include zirconium hafnium oxide, tungsten, tungsten nitride, tantalum nitride, titanium nitride, copper, aluminum, silver, and the like. Other layers that can be formed include zirconium oxide, silicates, or any suitable ternary compound.
The process of the present invention can be varied depending upon the particular type of material to be deposited on the substrate. For example, in one embodiment, the precursor fluid can be converted into the solid coating using only light energy. The light energy can be intermittently emitted into the reaction chamber in substantial synchronization with the pulsating precursor fluid. In order to ensure that substantially no precursor fluid remains in the reaction chamber after a single pulse, an inert gas can be introduced into the reaction chamber in between the pulses of the precursor fluid. The inert gas, which can be, for instance, argon, helium, or nitrogen, can purge from the reaction chamber any precursor fluid not converted into a solid material.
In another embodiment of the present invention, the substrate can be heated by an electrical resistance heater placed adjacent to the substrate during the deposition process to assist in formation of the solid coating. For example, the precursor fluid can be pulsed into the reaction chamber and converted into a solid coating on the substrate as the substrate is heated by the resistance heater. After formation of the solid layer, the layer can then be exposed to light energy in order to repair defects that may have formed or to stabilize the stoichiometry of the layer.
In another embodiment, the precursor fluid can be pulsed into the reaction chamber and immediately exposed to light energy for forming the solid layer. After each pulse, the light energy sources can be decreased or turned off and the reaction chamber can be purged with an inert gas. If desired, the inert gas can be introduced into the chamber at a temperature lower than the substrate in order to assist in cooling the formed layer. After the inert gas has purged any remaining precursor fluid not converted Into a solid material, the light energy sources can once again be activated in order to anneal the formed layer. This process can then be repeated in order to build up the thickness of the layer. Such an alternative heating and deposition process results in a pin hole free film.
For most applications, preferably the process of the present invention is desirably carried out in a cold wall reaction chamber. As used herein, a cold wall reaction chamber refers to a reaction chamber in which the walls are maintained at a temperature lower than the heated substrate. For Instance, the walls can be made from a insulating material that does not substantially heat up when exposed to light energy. Alternatively, the walls of the reaction chamber can be cooled, such as by circulating a cooling fluid through or around the walls of the chamber.
Other features and aspects of the present invention are discussed in greater detail below.